1. Field of the Invention
The present invention relates to a suspension device.
2. Description of the Related Art
Among various devices for suspension of axles from a frame, a suspension device comprising laminated spring leaves has been prevailing for vehicles such as trucks since it is simple in structure, inexpensive in cost, high in strength and highly durable.
FIG. 1 shows a conventional leaf-spring suspension device in which reference numeral 1 denotes a pair of left and right side rails extending longitudinally or in a fore-and-aft direction of a vehicle and providing part of a chassis frame; 2A and 2B, laminated spring leaves arranged along each of the side rails 1; and 3, an axle in the form of a beam member. The axle 3 is connected from below to longitudinally intermediate portions of the spring leaves 2A and 2B, using U-bolts 4.
The spring leaves 2A and 2B have front ends upwardly wound into eyes 5A and 5B, respectively, for pivotal motion about a spring pin 7 of a front bracket 6 secured to the side rail 1.
The upper spring leaf 2A has a rear end upwardly wound, just like its frond end, into an eye 8A for pivotal motion with a spring pin 11 of a shackle 10 about a rear bracket 9 secured to the side rail 1. Expansion and contraction of the spring leaves 2A and 2B in the fore-and-aft direction due to arched deflection of the same are absorbed or accommodated by the pivotal movement of the shackle 10.
At the carried position of the axle 3 by the spring leaves 2A and 2B via the U-bolts 4, a bracket 12 is also fixed by the U-bolts 4. A tip end of the bracket 12 is connected by a shock absorber 13 to the side rail 1 arranged just above the bracket 12.
This kind of leaf-spring suspension device has been disclosed, for example, in JP 2004-306805A.
In the conventional device, the spring leaves 2A and 2B are deflected at vertically unaligned positions so that relative displacement is inevitably caused between the leaves 2A and 2B upon such deflecting, resulting in metal-to-metal contact at front and rear ends of the spring leaves 2A and 2B. Thus, a greater frictional resistance is produced to produce a greater reaction force tending to constrain the relative displacement between the spring leaves 2A and 2B so that the leaves 2A and 2B become less deflectable, resulting in difficulty in satisfactorily lowering the spring constant and thus difficulty in satisfactorily improving comfort of the vehicle ride.
Accommodation of the expansion and contraction of the spring leaves 2A and 2B in the fore-and-aft direction upon deflecting of the same by pivotal movement of the shackle 10 causes the axle 3 to have a slantwise rearward ascending trajectory; thus, when the vehicle body has roll motion upon cornering of the vehicle, the axle 3 is displaced rearward and forward on vehicle-body sinking and floating sides transversely of the vehicle, respectively, resulting in occurrence of axle or roll steer which may adversely affect the driveability.
The invention was made in view of the above and has its object to provide spring leaves more deflectable than ever before for improvement in comfort of the vehicle ride and suppressing the occurrence of the axle or roll steer upon roll motion for improvement of the driveability.